This chapter analyzes potential mistakes and pitfalls that should be avoided during A/B testing. A/B testing can help even the smallest of organizations and sites, but it becomes more powerful the more traffic a site has. If the website is starved for traffic, A/B testing probably should not be the first priority. Using A/B testing to learn about how visitors engage with certain types of content or color or messaging can be illuminating and can feed back into later conversations with organization's brand team or the global site design team. Testing occasionally reveals a change that increases one metric but decreases another. It is suggested to consider whether there is willingness to test a page variant that is in some way off-brand or one that would not necessarily be picked for a quick roll out to all users should it win the test.